Apple has updated information on the Apple Watch. According to their website, the Apple Watch is “splash and water resistant but not waterproof. You can, for example, wear and use Apple Watch during exercise, in the rain and while washing your hands, but submerging Apple Watch is not recommended. ”
Apple Watch has a water-resistance rating of IPX7 under IEC standard 60529. According to that standard:
“Withstands incidental exposure to water of up to 1 meter for up to 30 minutes.”
Apple doesn’t mention anything regarding showering. Based on this rating, it should in theory be ok. Tim Cook was quoted as saying he showers with is Apple Watch. I’d wait from clarification from Apple on this before testing. If you opt for a leather band, that is most definitely not water resistant.